Field of the Invention
The present invention relates to an apparatus for and a method of plating a surface of a workpiece (substrate) such as a semiconductor wafer, and more particularly to a plating apparatus and a plating method which are suitable for forming plated films in fine inte+--rconnect trenches, holes, or resist openings defined in a surface of a substrate, or forming bumps (protrusive electrodes) to be electrically connected to electrodes of a package or the like on a surface of a substrate. For three-dimensionally packaging of semiconductor chips or the like, it is necessary to form a number of through via plugs in substrates which are referred to as interposers or spacers. The plating apparatus and the plating method according to the present invention are also used to fill via holes for forming such through via plugs. More specifically, the present invention is concerned with a dip-type plating apparatus and a dip-type plating method for plating a substrate held by a substrate holder by immersing the substrate in a plating solution in a plating tank.
Description of the Related Art
Apparatus for plating substrates are generally classified into face-down type plating apparatus and dip-type plating apparatus.
A face-down type plating apparatus performs plating of a substrate such as a semiconductor wafer while the substrate is being held horizontally by a head with its surface to be plated facing downwardly. The substrate is normally housed in a carrier receptacle such as an FOUP (Front Opening Unified Pod) or the like while the substrate is being held horizontally with its surface to be plated facing upwardly. Therefore, before the substrate is plated by the face-down type plating apparatus, the substrates needs to be turned upside down within the face-down type plating apparatus.
On the other hand, a dip-type plating apparatus performs plating of a substrate which is held by a substrate holder by bringing the substrate vertically into a plating solution in a plating tank. Therefore, it is necessary to keep the substrate holder horizontal when the substrate is to be held in the substrate holder, and to keep the substrate holder vertical when the substrate is to be immersed in the plating solution. Consequently, the dip-type plating apparatus has a mechanism for turning a substrate from a vertical state into a horizontal state and also for turning a substrate from a horizontal state into a vertical state.
As shown in FIG. 33, for example, a conventional plating apparatus has an arm 304 rotatably mounted on a transporter 300 by a motor 302. After the arm 304 clamps an end of a substrate holder 306, the motor 302 is energized to turn the arm 304 vertically through 90° to turn the substrate holder 306 from a vertical state into a horizontal state. The substrate holder 306 is then placed horizontally on a table 308. As shown in FIG. 34, another conventional plating apparatus has a fixing station 316 including a vertically rotatable table 310 and a rotational shaft 314 which clamps an end of a substrate holder 312 and rotates the substrate holder 312. The rotational shaft 314 is rotated about its own axis to turn the substrate holder 312 from a vertical state into a horizontal state.
As recent years have seen substrates of greater sizes, mechanisms for rotating arms or tables for use with such substrates have become larger in size, and the time required to turn substrate holders from a vertical state into a horizontal state and also from a horizontal state into a vertical state tends to become longer. The larger mechanisms for rotating arms or tables need a greater space required to turn the arms or the tables in plating apparatus. As a result, the plating apparatus themselves are larger in size and more expensive to manufacture.
The conventional plating apparatus also include a substrate holder opening and closing mechanism, i.e., a fixing robot, which is used to set a substrate on a substrate holder. The substrate holder opening and closing mechanism has been suffering the following problems:
A plating apparatus, which includes a substrate holder for holding a substrate vertically and immersing the substrate in a plating solution, is known. In this plating apparatus, the substrate holder holds the substrate by gripping the substrate between a fixed supporting member and a movable supporting member that can be opened and closed about a hinge. The movable supporting member has a rotatable support member which is not detachable. When the support member is rotated to slide an outer circumferential portion thereof into a clamper of the fixed supporting member, a seal ring of the movable supporting member seals the outer circumferential edge of the substrate and certain areas of the fixed supporting member, making it possible for electric power feed contacts of the fixed supporting member to contact the outer circumferential edge of the substrate (see Japanese patent No. 3979847, Japanese patent No. 3778282, Japanese patent No. 3940265, and Japanese patent No. 4162440).
According to the above-described plating apparatus, when the support member rotates, it causes wear on itself, and also causes the movable supporting member to rotate, possibly displacing the substrate out of positional alignment and impairing the sealing capability of the seal ring. To avoid such drawbacks, a pressing rod is applied to press the movable supporting member, and the support member is rotated while reducing wear on the support member with the pressing rod. However, for rotating the support member while reducing wear on the support member, the plating apparatus requires a complex mechanism which is vertically reciprocally movable along a vertical axis and which is also rotatable. The complex mechanism makes a substrate holder opening and closing mechanism complex in structure. The complex substrate holder opening and closing mechanism takes up a large space in the plating apparatus, making the plating apparatus large in size and expensive to manufacture.
Another problem with the conventional substrate holder opening and closing mechanism is that if the substrate holder has a different thickness, then the distance that the pressing rod presses the seal ring against the substrate holder tends to vary. Specifically, if the substrate holder is thinner than its normal thickness, then since the seal ring is not sufficiently compressed, the support member is liable to wear more upon rotation. If the substrate holder is thicker than its normal thickness, then the seal ring is excessively compressed and damaged. Accordingly, the substrate holder, which is not properly fabricated to meet its thickness requirement, is responsible for lowering the sealing capability of the seal ring.
The conventional substrate holder opening and closing mechanism generally incorporates a positional displacement detecting measure for detecting when the substrate is displaced out of positional alignment at the time it is mounted in the substrate holder. According to this positional displacement detecting measure, a substrate guide is disposed on the fixed supporting member at a position near the outer circumferential edge of the substrate. A horizontal light sensor, such as a photosensor or laser sensor, measures the amount of light from a light beam that is applied horizontally over the substrate in the substrate holder. If the substrate is placed on the substrate guide, then the substrate is tilted and blocks the light beam. Therefore, the amount of light detected by the horizontal light sensor is made smaller than if the substrate is properly set in the substrate holder clear of the substrate guide. In this manner, positional displacements of the substrate in the substrate holder are detected based on a reduction in the detected amount of light. When the substrate is displaced out of positional alignment in the substrate holder, the substrate guide keeps the substrate thereon and holds the substrate tilted, preventing the substrate from staying in a horizontal plane out of positional alignment.
However, the horizontal light sensor is problematic in that it may erroneously detect the substrate as being displaced out of positional alignment in the substrate holder when there is a water droplet on the substrate, the substrate is warped itself, the substrate holder is warped itself, a table on which the substrate holder is placed is warped itself, or the substrate holder is tilted by dust or dirt particles applied to the table on which the substrate holder is placed. The horizontal light sensor also suffers a problem as to its detection accuracy because the substrate guide has its height limited by the size of the substrate holder and the amount of light that can be detected by the sensor tends to decrease with time on account of smear-induced fogging on the surface of the sensor due to use over time.
In the dip-type plating apparatus, the substrate holder thereof is stored in a stocker therefore before it operates. When the dip-type plating apparatus starts to operate, the substrate holder is taken out of the stocker, and a substrate to be processed is taken out of its storage and held by the substrate holder. The substrate holder, which is holding the substrate, is transported by a substrate holder transporter to the plating tank and other processing tanks associated with the plating process, where the substrate is processed accordingly.
When the substrate holder is found as suffering a trouble such as an electric feeding failure or the like and is to be serviced to remove the trouble, the conventional dip-type plating apparatus has to be shut down and hence its operation availability is lowered. The substrate holder, which is found as suffering an electric feeding failure, is returned to the stocker and inhibited from use until it is serviced. While the dip-type plating apparatus is operating in a plating process, access to the interior of the dip-type plating apparatus is limited for safety reasons. Consequently, when the substrate holder is to be serviced, it is necessary to wait until at least the plating process which has started immediately prior to the trouble. Since the substrate holder, which is inhibited from use, cannot be used in a plating process, the throughput of the dip-type plating apparatus per unit time is reduced.
In the conventional dip-type plating apparatus, the stocker for storing the substrate holder is inseparably incorporated in the apparatus. When the substrate holder placed in the stocker needs to be serviced, the substrate holder is manually removed from the stocker or removed from the stocker by a dedicated hoist. Alternatively, the stocker is carried to a delivery tank or a service area, which is accessible from outside of the dip-type plating apparatus, within the dip-type plating apparatus, and then the substrate holder is manually removed from the stocker or removed from the stocker by a dedicated hoist. It has been tedious and time-consuming to remove the substrate holder from the dip-type plating apparatus and return the substrate holder into the dip-type plating apparatus. The tedious and time-consuming servicing process has been becoming worse because the manual labor required increases and the hoist used becomes larger in size as substrates to be handled are larger in size.